The longitudinal swelling of three different sorts of wools, when permanently set, has been studied. It has been observed that, when progressively set, Mohair fibers, which acquire a set much more readily, show retarded swelling, compared to Blackface wool fibers. The effect of setting time reveals that the structure of Mohair fiber opens up at a much faster rate, but the swelling is high in the case of Blackface wool fiber which exhibits poor settability. Moreover, in each case, fibers, on acquiring a certain set, show a decrease in longitudinal swelling due to bond re-formation. It appears that the increase in longitudinal swelling, which is due to changes in the cortical regions, is influenced not only by the setting strain or the setting time; the number of strained bonds initially present and the ease of bond re-formation also determine the extent of swelling.
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